IGF-1 LR3 (Insulin-like Growth Factor 1 Long Arg3) is a synthetic form of IGF-1, a protein that plays a key role in growth, development, and cellular repair. It’s similar to the naturally occurring IGF-1 in your body but has a longer half-life due to a modification in its structure—specifically, the substitution of the amino acid arginine at position 3. Because of this modification, IGF-1 LR3 stays in the bloodstream for a longer period of time, allowing for more extended biological effects. It’s often used in the bodybuilding and fitness community for its potential to promote muscle growth, increase fat loss, and improve recovery.